Comparison ofE TestwithAgarDilution forAntimicrobial Susceptibility Testing ofNeisseria gonorrhoeae

Acollection of150Neisseria gonorrhoeae isolates fromAfrica, wherevarious resistance mechanisms among N.gonorrhoeae isolates arecommon, wasusedtothecompare E test(ABBiodisk, Solna, Sweden) withagar dilution susceptibility testing. MICsobtained bytheE testagreed within 1log2 concentration bytheagar dilution methodfor97.5, 97.3, 96.6, 94,and84.7%ofthetested isolates forpenicillin, ciprofloxacin, chloramphenicol, tetracycline, andtrimethoprim-sulfamethoxazole, respectively. Nosignificant difference in susceptibility categorization wasobserved between either method. TheEtest isanattractive alternative tothe agardilution technique andisa moreappropriate methodforN.gonorrhoeae susceptibility testing in developing countries. An important andessential measureformonitoring the effectiveness ofrecommended drugsforthetreatment of gonorrhoea issurveillance oftheinvitro antimicrobial susceptibilities ofclinical isolates ofNeisseria gonorrhoeae (2, 5). The antimicrobial susceptibility patterns ofN.gonorrhoeae may change rapidly, especially inareas whereineffective treatment regimens areapplied (10), andantimicrobial resistance inN. gonorrhoeae maybemediated byplasmids orchromosomal mechanisms (4, 6).Whereas plasmid-mediated penicillin resistance caneasily bedetected byrapid andinexpensive tests for 1-lactamase andplasmid-mediated tetracycline resistance can bedemonstrated bydiskdiffusion susceptibility testing orby growing gonococcal isolates onculture mediumcontaining 10 ,ugoftetracycline perml(9), themethods required toidentify chromosomally mediated resistance aremorelaborious, expensive, anddifficult tostandardize. Therecommend procedureforantimicrobial susceptibility testing ofgonococci is determination oftheMICsbyanagardilution technique (12). However, this methodiscumbersome, isdifficult tostandardize, andisperformed onlyinresearch laboratories, mainly in industrialized countries. TheE test(ABBiodisk, Solna, Sweden) isa recently developed technique forquantitative (MIC)antimicrobial susceptibility testing (1). Itconsists ofaplastic carrier strip withapredefined continuous exponential antibiotic gradient immobilized ononeside; itisapplied ontothesurface ofan inoculated agarplate. Ifaccurate, thismethodmaybea potential alternative andamoreappropriate methodthanthe agardilution technique forMICdetermination forN.gonorrhoeae bylaboratories indeveloping countries, whereresistanceofgonococci toantimicrobial agents isamajorpublic health problem. Inthepresent study, antimicrobial susceptibility testing was performed byusing, inparallel, theEtest andtheagardilution methodtotestN.gonorrhoeae isolates fromtwoAfrican countries. Onehundred fifty recent clinical isolates ofN.